Low pressure reverse osmosis and nanofiltration processes are developed for new water resources. It was possible to separate dilute solution at operational pressure of below 0.5atm with the volume flux of 0.1m/d. Pollutants of ground water such as nitrate, organochloric compounds, metals are studied for model substances. Phenolic compounds and volatile organochloric compounds generally gave lower retentions compared to chloride ions while heavy metals gave higher retention. Size of solutes was plotted against rejection and correlation was discussed.High pressure reverse osmosis and nanofiltration processes are developed assuming 75% fresh water recovery process from 3wt% artificial sea water. Reflection coefficient, solutes permeation coefficient and pure water permeability was determined from experimental results. Process simulation was done for high recovery desalination process.Mechanism of solute separations in nanofiltration membranes were studied. The reason of lower rejection of nitrate compared to that of chloride was focused. Extended Nernst Plank equation was applied for the transport inside charged membrane and Donnan equilibrium condition was assumed for the surface of membrane. Partition coefficient was introduces because conventional theory fails to explain the phenomena.